The fate of the photoisomers of some chlorinated cyclodiene insecticidal chemicals, namely, photodieldrin, photoaldrin, photoisodrin, photoheptachlor and photochlordene in ecosystems is being investigated. The absorption, accumulation, metabolic disposition and elimination of these chemicals in food chain organisms at various trophic levels (plant; algae; microcrustacea, fish; birds, pigeon; mammals, mice and rats) is being studied. The in vivo and in vitro metabolites of photodieldrin, photoaldrin and photoisodrin are being characterized. The toxicity of these metabolites to insects, microcrustacea, fish and mice will be determined. Enzyme system(s) responsible for the metabolism of cyclodienes and their photoisomers are being characterized in insects and vertebrates. Both qualitative and quantitative diferences in metabolism of these chemicals have been observed. Such species-specific differences in absorption, metabolism, retention and elimination of these photoisomers will provide precise information about the ecological and health effects of cyclodienes and their terminal residues' (photoisomers).